High gravity 5gal efficiency challenges...but why doesn't that hurt 10gal batches too?

[stealthfixr]

A question for you mashing experts out there...why does efficiency drop so drastically when mashing a high gravity beer, but a similar amount of malt & water for a 'double size' batch results in normal efficiency...why?

Brewed an Imperial Stout on my Brewzilla 65L Gen 4 yesterday, using a full 21lb of malt & 1.5lb sugar and shooting for a 1.107 OG and 5.25gal batch size. That OG was using an assumption of 70% efficiency, which is 7-8 points lower than normal. What I got was shocking...about 60% efficiency with a 1.090 OG. While efficiency losses are common with high gravity beers, what occurred to me was that this batch in some ways was not that different than a 10gal one. A 10gal lager batch would use almost the same amount of malt, uses a similar amount of water, but boils for less time than the 90-min boil I used on the Imp Stout. But, the 10gal batch efficiency will be in the high 70s, much higher than the Imperial Stout that I just did.

One of the explanations for the high gravity efficiency losses is the thick grist to water ratio. While the Imp Stout grist was more thick than a 10gal lager batch, it was not vastly different. And, I question whether that is the only reason for the massive efficiency differences. The Stout boiled for a lot longer to get down to a 5.5gal volume, but that would not effect efficiency. The clear difference is in the volume and gravity of the resulting beers, but how does that effect efficiency when mashing?

 

[TheMadKing]

A few of your fundemental assumptions are incorrect.

The 10 gallon batch uses (roughly) twice as much water and twice as much grain to produce the same OG as a 5gallon batch.

It's a function of the target original gravity of the wort not of the amount of grain. A 10 gallon batch targeting a 1.107 OG would have roughly the same efficiency as a 5 gallon batch with the same target.

A longer boil does boost efficiency indirectly as well. A higher preboil volume requirement results in more sparging which boosts lauter efficiency.

 

[stealthfixr]

Yesterday's 5.5 gal Imp Stout used 21lb malt and 9.3gal water, plus 0.8gal sparge. Boiled for 90 minutes.

My 10-gal lager batches use ~21lb of malt and 10+gal of water to start with, then sparge with 0.8gal water. Boil 45-30 minutes, then add 2gal top-off water into the fermentor to make 10.5gal in the conical.

Not as stark a difference as a 'double' sized batch would suggest, mash wise...yet a massive difference in efficiency. Does the amount of sugars in the wort inhibit efficiency beyond a certain amount?

 

[TheMadKing]

Yesterday's 5.5 gal Imp Stout used 21lb malt and 9.3gal water, plus 0.8gal sparge. Boiled for 90 minutes.

My 10-gal lager batches use ~21lb of malt and 10+gal of water to start with, then sparge with 0.8gal water. Boil 45-30 minutes, then add 2gal top-off water into the fermentor to make 10.5gal in the conical.

Not as stark a difference as a 'double' sized batch would suggest, mash wise...yet a massive difference in efficiency. Does the amount of sugars in the wort inhibit efficiency beyond a certain amount?

Your 10 gallon batches at what OG?

21lbs of grain in a 5 gallon batch makes 1.107 OG.

21 lbs of grain in a 10 gallon batch makes a much lower OG (I'm going to guess 1.060 without using a calculator to check.)

Your 10 gallon mash efficiency is higher because you are going to be sparging with much more water to get to your preboil gravity.

Let's walk through an example, I'm just pulling all these numbers out of the air for illustration they aren't real:

Lets say you mash at 2qt per pound for both the 5 gallon batches and 10 gallon batches and then run off each mash to a separate kettle (you're batch sparging in this example). You now have the same amount of first runnings and the same gravity of wort in both kettles.

For the 5 gallon batch you'll do a batch sparge of say 4 gallons to reach your preboil volume of 7.5 gallons. This results in a preboil gravity of 1.095, lets say. There is still considerable sugar left in your grain.

For the 10 gallon batch you now need to do two batch batch sparges of 4 gallons each to reach your preboil volume of 11.5 gallons. This results in a preboil gravity of 1.050.

You boil both down to 5 gallons and 10 gallons respectively and end up with an OG of 1.107 for the 5 gallon batch and 1.060 for the 10 gallon batch. So you can see from this example that the batch size doesn't matter, the only thing that matters is the amount of grain relative to the amount of sparge water you're using.

You can considerably boost the efficiency of a high gravity 5 gallon batch by doing a 2-3 hour boil. This forces you to sparge much more to reach the preboil volume you need so you increase your efficiency.

Edit: just a note, 0.8 gallons of sparge water is a tiny amount. You'll boost your efficiency by mashing with as little water as you need. A typical 1.050 gravity beer for me needs about 4 gallons of sparge water. The higher the gravity the more is needed in the mash so the less sparge water you have available.

 

[hottpeper13]

The most efficient mash is to have sparge liquor = to or > then mash liquor.
I get around 6% more when I dunk sparge my BIAB then when I do a full volume no sparge batch.

 

[DBhomebrew]

Most efficient mash will have 1st running ~= 2nd running. Well-performed, a single dunk or batch sparge will be ~8% more efficient than a no sparge.

But this isn't really what OP is asking about. They're comparing apples and oranges.

 

[DBhomebrew]

The clear difference is in the volume and gravity of the resulting beers, but how does that effect efficiency when mashing?

You're really looking at lauter efficiency, let's assume conversion efficiency at 100%.

In layman's terms, lauter efficiency is the ratio of how much wort makes its way into the kettle vs the amount of wort left in the grain bed.

For two batches of the same pre-boil volume, a larger grist (higher OG) will retain more wort in relation to pre-boil volume thereby reducing lauter efficiency. A higher percentage of the total wort volume remains in the grain (absorption or loss-to-grain ratio).

Compare a 5 gallon batch with 21lbs to a 10 gallon batch with 42lbs, their efficiencies should be roughly the same.

Compare a 5 gallon batch with 21lbs to another 5 gallon batch with 10.5lbs, and the lower OG batch will have a higher efficiency. Roughly the same efficiency you found on your 11 gallon 21lb batch.

It's a matter of (pre-boil volume) : (grist size).

 

[doug293cz]

Most efficient mash will have 1st running ~= 2nd running. Well-performed, a single dunk or batch sparge will be ~8% more efficient than a no sparge.

But this isn't really what OP is asking about. They're comparing apples and oranges.

This is true for a single batch sparge process. For multiple batch sparges, or fly sparging, lower strike water volumes (and lower first runnings volume) will have higher efficiencies. For multiple batch sparges, or fly sparging, you have to worry about potential over-sparging, but this is not usually a concern with single batch sparge.

Brew on

 

[doug293cz]

Here's a chart that shows what happens to lauter efficiency as the grain bill to pre-boil volume ratio increases for various sparge counts and grain absorption rates. 0.12 gal/lb is typical for a traditional mash tun, and 0.06 gal/lb can be obtained with a squeezed BIAB process. A fly sparge can be equivalent to a 3 - 6 batch sparge process, depending on how well it is executed.

The calculations assume equal volumes and grain absorption rates for all run-offs, subject to the constraint that mash thickness not be greater that 1.0 qt/lb (this limits sparge volumes for larger grain bills, and makes sparge run-off volumes less than first runnings volume.)